1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to a method for manufacturing a pad region of an LCD device.
2. Discussion of the Related Art
In general, an LCD device according to a related art includes a lower substrate having a TFT and a pixel electrode, an upper substrate having a color filter film for displaying colors and a common electrode, and a liquid crystal film between the lower and upper substrates.
The LCD device according to the related art will now be described in more detail.
FIG. 1 is a layout of a TFT array region and a pad region in a lower substrate of a general LCD device.
To define a plurality of pixel regions, a plurality of gate lines 100 are formed on the lower substrate (not shown) at constant intervals, and a plurality of data lines 200 are formed perpendicular to the gate lines 100 at constant intervals. Then, a plurality of TFTs (thin film transistors) are formed at crossing points of the plurality of gate and data lines 100 and 200.
In each TFT, a gate electrode 2a projects from the gate line 100, and a semiconductor film 4 in an island shape is formed above the gate electrode 2a. A source electrode 6 projects from the data line 200 toward the semiconductor film 4, and a drain electrode 7 is formed in a portion where the source and drain electrodes 6 and 7 oppose each other. A pixel electrode 9a made of ITO is electrically connected to the drain electrode 7 of the TFT in the pixel region.
Although not shown, a plurality of black matrix films are formed, except in the pixel regions, to prevent light leakage from the upper substrate. Then, R/G/B color filter films are formed in the pixel regions between the black matrix films for displaying colors. A plurality of common electrodes are formed on the entire surface of the upper substrate including the color filter films.
Then, the lower and upper substrates are attached to each other with a certain constant distance therebetween, and then a liquid crystal is injected between the lower and upper substrates.
The above LCD device adjusts display conditions by applying a certain voltage to both ends of the lower and upper substrates. A conductive material that does not intercept light has to be deposited on the surfaces of the upper and lower (glass) substrates. Therefore, transparent electrodes are formed on the lower and upper substrates by sputtering. At this time, the common electrodes discussed above are formed on the upper substrate and the pixel electrode is formed on the lower substrate.
In the related art LCD device, the transparent electrode is formed of an indium tin oxide (ITO) film or SnO2 film The ITO film obtains high conductivity, chemical stabilization and thermal stabilization. Furthermore, the ITO is easy to pattern, so that the ITO film as the transparent electrode can be used in both segment and dot matrix. The SnO2 film obtains chemical stabilization and physical strength more than the ITO film, but its conductivity is less than that of the ITO. The SnO2 film also has a problem of forming the electrode by photolithography. As such, the SnO2 Film can not be used as the transparent electrode of a minute pattern in which a low resistance is required.
In general, the ITO film as the transparent electrode provides a low manufacturing cost, a good adhesion to the substrates and photoresists, a low resistance, a high transmittivity, and a uniformity of resistance value, transmittivity and etching ratio. The ITO film as the transparent electrode is also needed not to have an etching residue during the formation of a minute pattern, and is required not to have particles or defects on the surfaces certain layers.
FIG. 2 is a sectional view showing a structure of the related art LCD device taken along line I–I′ (TFT region) and line II–II′ (pad region) of FIG. 1.
As shown in FIG. 2, in the TFT region, a gate electrode 2a is formed on a lower glass substrate 1, and then a gate insulating film 3 is formed on the entire surface of the glass substrate 1 to cover the gate electrode 2a. 
A semiconductor film 4 is formed on the gate insulating film 3 above the gate electrode 2a, and then source/drain electrodes 6 and 7 are formed at both sides of the semiconductor film 4. An ohmic contact film 5 is formed between the semiconductor film 4 and the source/drain electrodes 6 or 7.
A passivation film 8 having a contact hole 8a to expose the drain electrode 7 is formed over the glass substrate 1. A pixel electrode 9a is electrically connected with the drain electrode 7 through the contact hole 8a. 
In the pad region, a gate pad 2b or a data pad 2c is formed of the same material as a gate line or a data line. As an example, FIG. 2 illustrates the gate pad 2b. The gate insulating film 3 is formed on the glass substrate 1 to cover the gate pad 2b, and then the passivation film 8 having a contact hole 8b to expose the gate pad 2b is formed on the gate insulating film 3. A pad contact film 9b is formed of the same material as the pixel electrode 9a on the gate pad 2b. 
As shown in FIG. 2, in the related art LCD device, the gate insulating film 3 and the passivation film 8 are formed of a silicon nitride film. The source/drain electrodes 6 and 7, the gate electrode 2a and the gate pad 2b are formed of a conductive metal such as Cu or Ti. The pixel electrode 9a and the pad contact film 9b are formed of a transparent conductive film such as ITO.
A method for manufacturing the related art LCD device of FIG. 1 will now be described as follows.
A gate electrode material such as Al, Cr or Al alloy is deposited on the entire surface of the substrate 1 by sputtering, and a photoresist (not shown) is deposited. Then, the gate line 100, the gate electrode 2a and the gate pad 2b are formed by photolithography. A silicon nitride film SiNx or a silicon oxide film SiOx is deposited on the entire surface of the substrate 1 including the gate line 100, the gate electrode 2a and the gate pad 2b by a plasma enhanced chemical vapor deposition (PECVD), thereby forming the gate insulating film 3.
The semiconductor film 4 and the ohmic contact film 5 are sequentially deposited over the substrate 1, and then patterned to remain on the gate electrode 2a and the gate insulating film 3.
Subsequently, Al, Cr or Al alloy is deposited over the substrate 1 by sputtering and then is selectively removed to pattern the data line 200 and the source/drain electrodes 6 and 7. Then, the ohmic contact film 5 is removed between the source and drain electrodes 6 and 7.
The passivation film 8 is formed on the entire surface of the substrate including the source and drain electrodes 6 and 7. Then the passivation film 8 and the passivation/gate insulating films 8 and 3 are selectively removed to respectively expose the drain electrode 7 and the gate pad 2b of the pad region through the contact holes 8a and 8b. 
A polycrystal ITO is deposited on the entire surface of the substrate including the contact holes by sputtering, and then is patterned, so that the pixel electrodes 9a connected to the drain electrode 7 is formed in the TFT region, simultaneously, the pad contact film 9b connected to the gate pad 2b is formed in the pad region. At this time, the polycrystal ITO is deposited at a thickness of 500 Å.
However, the related art LCD device has the following problems.
The pixel electrode and the pad contact film are formed of polycrystal ITO, so that a stripper diffuses and penetrates a grain boundary of the polycrystal ITO during a removal of the photoresist by patterning the pixel electrode and the pad contact film. Therefore, the stripper generates a galvanic effect with the pad, so that miniature gaps are formed at an interface between the pad contact film and the pad region, causing a contact failure indicated as reference numeral 10 in FIG. 2. It can also cause a change in TFT characteristics and a degraded yield.